udevadm: Propagate return code from verb result

udevadm lock did not propagate the return code from the child process
because all positive values were treated as success.

v2:
Now 'udevadm test-builtin' ignores all positive return values from the
builtin commands. Otherwise, as the hwdb builtin returns an positive value
when a matching entry found, 'udevadm test-builtin hwdb' will fail.

v3:
Initialize partition table before calling 'sfdisk --delete'.

Co-authored-by: Yu Watanabe <watanabe.yu+github@gmail.com>

test/units/testsuite-64.sh

@@ -396,6 +396,11 @@ EOF
 
     udevadm control --reload
 
+    # initialize partition table
+    for disk in {0..9}; do
+        echo 'label: gpt' | udevadm lock --device="${devices[$disk]}" sfdisk -q "${devices[$disk]}"
+    done
+
     # Delete the partitions, immediately recreate them, wait for udev to settle
     # down, and then check if we have any dangling symlinks in /dev/disk/. Rinse
     # and repeat.